Evaluation of thermomechanical pretreatment for enzymatic hydrolysis of pure microcrystalline cellulose and cellulose from Brewers’ spent grain

Microcrystalline cellulose (Avicel PH102) and Brewers’ spent grain (BSG) were subjected to Détente Instantanée Contrôlée (DIC) thermomechanical pre-treatment before exposure to cellulases (Celluclast 1.5 L). In a first part, we showed that the addition of β-glucosidase (Novozym-188) increased the hydrolysis yield of Avicel. A maximal theoretical yield (100%), was obtained for 5 and 10 g/L of Avicel using a mixture of Celluclast 1.5 L/Novozym-188. After DIC pre-treatments, the initial rate and final yield of hydrolysis decreased in comparison with those from untreated microcrystalline cellulose. This phenomenon may be due to the modification of the crystallinity of pure cellulose and the formation of inhibitors during the pre-treatment. In a second part, BSG was thermomechanically pre-treated and hydrolyzed. The results showed that the hydrolysis yield of BSG treated at pressure levels between 2 and 7 bar during 15 min was strongly improved compared to hydrolysis yield of untreated BSG. The optimized hydrolysis process, under intensive DIC conditions, achieved a glucose yield corresponding to 100% of the theoretical cellulose value. The morphology of BSG samples was studied with Scanning Electronic Microscopy (SEM) and highlighted that the structure of pre-treated BSG showed an important disruption compared to the rigid structure of untreated BSG.